A typical class of operational amplifiers is the class having a differential input and a single ended output. Ideally, the inputs may receive any D.C. common-mode voltage. However, realistically, the input voltage differential of an operational amplifier must be within the input common-mode voltage range. Since the output is single ended, the output voltage is always referenced with respect to a ground potential. However, a more general class of operational amplifiers is the class which has a differential input and a differential output. In certain integrated circuit signal processing applications, the class of fully differential operational amplifiers maximizes power supply rejection much more than the class of single ended output operational amplifiers. Again, the common-mode D.C input voltage may be any value within the input common-mode range. However, when differential outputs are present, the common-mode D.C. output voltage may be chosen to be any value within the output common-mode voltage range, independent of what the input common-mode voltage is. In order to maximize the dynamic range of the output voltage so that each signal can symmetrically vary as much as possible, the common mode D.C. output voltage commonly is at mid-supply. A disadvantage common to fully differential operational amplifiers is that such circuits are usually physically larger than single ended operational amplifiers and have a more complicated structure. Further, to effect a fully differential integrator requires two external integrating capacitors rather than one. A fully differential operational amplifier which uses common-mode feedback is described in "A Family of Differential NMOS Analog Circuits for a PCM Codec Filter Chip" by Senderowicz, Dreyer, Huggins, Rahim and Laber in the IEEE Journal of Solid-State Circuits, Volume SC-17, No. 6, December 1982, pages 1014-1023. A fully differential operational amplifier is described by Senderowicz et al. on page 1016. However, the operational amplifier utilizes switched capacitors requiring multiple clock signals to operate and a large amount of circuit area to implement.